Project Summary/Abstract: The primary role of the gustatory system is to subject food to be ingested to a quality control test to prevent the consumption of harmful compounds, while also regulating the intake of nutrients into the body. Perception of intensely bitter or sour taste identifies toxic or spoiled foods that should not be ingested; however, many beneficial compounds, such as oral pharmaceuticals and sugar substitutes also are perceived as bitter, resulting in patient non-compliance. Understanding the physiological regulation of these signaling pathways should lead to our enhanced ability to increase the palatability of therapeutics and sweeteners, thus enhancing compliance and overall health. Three taste modalities (umami, sweet, bitter) are detected by G protein-coupled receptors (GPCRs) - critical components of many bodily processes and the most common drug target in the human body. GPCRs function by associating with heterotrimeric G-proteins and initiating intracellular signaling cascades after activation by their cognate ligands. Multiple modulators, including the superfamily of 'regulators of G-protein signaling' (RGS proteins) that act as G-directed GTPase-accelerating proteins (GAPs), regulate G-protein activity and GPCR-initiated signaling; however, taste-specific modulators of G-proteins have not been definitively established. Two groups have previously identified at least one RGS protein as being expressed in lingual taste cells and have hypothesized that this RGS protein regulates tastant signal transduction; yet, the actual function of RGS proteins in these tastant-responsive cells is currently unknown. The overall aim of this proposal is therefore to gain a greater understanding of the role of RGS proteins in the regulation of tastant signal transduction. Aim 1 is to determine the expression of RGS proteins in relation to other tastant signaling components in taste-responsive tissues and cells, via RT-PCR and in situ hybridization techniques of detection. Aim 2 is to delineate the selectivity of these RGS proteins towards taste-specific G subunits in biochemical assays of binding and GTP hydrolysis acceleration. Aim 3 is to determine the effects of RGS proteins on tastant signaling outcomes in an integrated cellular system using readouts of second messenger production. Our results will help define the role of RGS proteins in shaping the duration and potency of tastant signaling.